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Commit 34a663a

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vil02appgurueu
andauthored
fix: hadnle zeros at the endpoints in BisectionMethod (#1640)
* fix: hadnle zeros at the endpoints * style: use simpler syntax express polynomials Co-authored-by: appgurueu <34514239+appgurueu@users.noreply.github.com> --------- Co-authored-by: appgurueu <34514239+appgurueu@users.noreply.github.com>
1 parent 702840b commit 34a663a

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2 files changed

+14
-13
lines changed

2 files changed

+14
-13
lines changed

‎Maths/BisectionMethod.js‎

Lines changed: 4 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -23,7 +23,7 @@ const findRoot = (a, b, func, numberOfIterations) => {
2323

2424
// Bolzano theorem
2525
const hasRoot = (a, b, func) => {
26-
return func(a) * func(b) < 0
26+
return func(a) * func(b) <= 0
2727
}
2828
if (hasRoot(a, b, func) === false) {
2929
throw Error(
@@ -45,10 +45,9 @@ const findRoot = (a, b, func, numberOfIterations) => {
4545
const prod2 = fm * func(b)
4646

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// Depending on the sign of the products above, decide which position will m fill (a's or b's)
48-
if (prod1 > 0 && prod2 < 0) return findRoot(m, b, func, --numberOfIterations)
49-
else if (prod1 < 0 && prod2 > 0)
50-
return findRoot(a, m, func, --numberOfIterations)
51-
else throw Error('Unexpected behavior')
48+
if (prod2 <= 0) return findRoot(m, b, func, --numberOfIterations)
49+
50+
return findRoot(a, m, func, --numberOfIterations)
5251
}
5352

5453
export { findRoot }

‎Maths/test/BisectionMethod.test.js‎

Lines changed: 10 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,7 @@
11
import { findRoot } from '../BisectionMethod'
22

33
test('Equation f(x) = x^2 - 3*x + 2 = 0, has root x = 1 in [a, b] = [0, 1.5]', () => {
4-
const root = findRoot(
5-
0,
6-
1.5,
7-
(x) => {
8-
return Math.pow(x, 2) - 3 * x + 2
9-
},
10-
8
11-
)
4+
const root = findRoot(0, 1.5, (x) => x ** 2 - 3 * x + 2, 8)
125
expect(root).toBe(0.9990234375)
136
})
147

@@ -35,3 +28,12 @@ test('Equation f(x) = sqrt(x) + e^(2*x) - 8*x = 0, has root x = 0.93945851 in [a
3528
)
3629
expect(Number(Number(root).toPrecision(8))).toBe(0.93945851)
3730
})
31+
32+
test('Equation f(x) = x^3 = 0, has root x = 0.0 in [a, b] = [-1.0, 1.0]', () => {
33+
const root = findRoot(-1.0, 1.0, (x) => x ** 3, 32)
34+
expect(root).toBeCloseTo(0.0, 5)
35+
})
36+
37+
test('Throws an error when function does not change sign', () => {
38+
expect(() => findRoot(-1.0, 1.0, (x) => x ** 2, 10)).toThrowError()
39+
})

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